Long-acting injectable formulations and crystalline forms of buprenorphine derivatives

ABSTRACT

This disclosure relates to crystalline forms of 3-acyl-buprenorphine derivatives and sustained release injectable pharmaceutical compositions for treatment of opioid dependence, pain or depression, including an aqueous suspension of crystalline 3-acyl-buprenoprhine, or a pharmaceutically acceptable salt thereof, wherein the composition does not include an organic solvent, a polylactide polymer, a polyglycolide polymer, or a copolymer of polylactide and polyglycolide. This disclosure also includes 3-acyl-buprenoprhine or a pharmaceutically acceptable salt thereof prepared in a controlled release matrix, including poly(lactide-co-glycolide), sucrose acetoisobutyrate, lecithin, diolein and a combination of two or more thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 16/981,745 filed on Sep. 17, 2020, which is a Section 371 National Phase of International application No. PCT/CN2019/086449, filed on May 10, 2019, which claims the benefit of priority under Section 119 to U.S. Provisional application Ser. No. 62/670,714 filed on May 11, 2018, the entire contents of all of which are incorporated herein by reference.

BACKGROUND Technical Field

The present disclosure relates generally to crystalline forms and formulations of buprenorphine derivatives. In particular, the present disclosure relates to an injectable composition comprising buprenorphine derivatives, or the metabolite or prodrug thereof, its uses, as well as methods of treatment using the same for opioid dependence, pain, and depression.

Background

Buprenorphine, (5α,7α(s))-17-cyclopropylmethyl)-α-(1,1-dimethylethyl)-4,5-epoxy-18,19-dihydro-3-hydroxy-6-methoxy-α-methyl-6,14-ethenomorphinan-7-methanol, is a derivative of thebaine, which belongs to the family of opioid alkaloids. The structure of buprenorphine is shown by the following formula (Formula I) with a molecular weight of 467.64:

As a partial and potent μ-receptor agonist, buprenorphine has a higher affinity to compete with other full agonists, such as morphine, methadone, etc. With 25 to 40 times higher potency than that of morphine, buprenorphine is indicated for the treatment of moderate to severe chronic pain, and pre-operative analgesia in several dosage forms, e.g., Buprenex® (intramuscular or intravenous injection), Norspan®, Butrans® (a transdermal patch), Temgesic® (a sublingual tablet), and Belbuca® (a buccal film). The therapeutic concentrations (C_(max)) of Butrans in healthy subjects range from 0.1 to 0.5 ng/mL, corresponding to a dose of 5 to 20 μg/hour. In addition, various products of buprenorphine hydrochloride are approved for treating opioid addiction in higher dosages, e.g., Subutex® (a sublingual tablet), Sublocade™ (a subcutaneous injection), and some are combination products of buprenorphine hydrochloride and naloxone hydrochloride, e.g., Suboxone® (a sublingual film, in a 4:1 ratio of buprenorphine hydrochloride and naloxone hydrochloride), Zubsolv® (a sublingual tablet), and Bunavail® (a buccal film). The therapeutic concentrations (C_(max)) of Suboxone range from 1 to 6 ng/mL, corresponding to a dose of 2 to 16 mg sublingual films.

Furthermore, buprenorphine is also a potent antagonist of the κ-opioid receptor, and this could result in the reduction of tolerance and has an antidepressant effect. Recently, buprenorphine is utilized in a combination product, ALK-5461, which consists of buprenorphine (a κ-receptor antagonist) and samidorphan (a μ-receptor agonist) and has been announced for an anti-depressant effect.

In previous studies, various buprenorphine derivatives were disclosed. Among them, modifications of the phenol group by forming ester bond linkages are more common. These ester derivatives are synthesized and compared with buprenorphine and the hydrochloride salt thereof. In 1995, Stinchcomb et al. published an article related to 3-alkyl ester derivatives of buprenorphine in Pharm. Res. (1995), 12, 1526-1529 (Formula II below, R=acetyl, propanoyl, butanoyl, pentanoyl, hexanoyl, heptanoyl). These derivatives were viewed as prodrugs and purported to improve the physiochemical characteristics of the parent compound to increase its relative permeability through skin in the following articles: Biol. Pharm. Bull. (1996), 19, 263-267 and Pharm. Res. (1996), 13, 1519-1523.

Thereafter, several C3-esterified buprenorphine derivatives and applications thereof have been disclosed in various patents. For example, U.S. Pat. No. 7,084,150, issued to Euro-Celtique S.A., describes a huge family of buprenorphine prodrugs and analogs, which include ester bonds or ether bond modified derivatives. EP Patent No. 1422230, issued to Jhi-Joung Wang, discloses dimerized derivatives of buprenorphine and similar alkylcarbonyl derivatives. Prodrug strategy and oil carrier of these derivatives were introduced by an intramuscular or subcutaneous injection, which displays prolonged analgesia actions for 5 hours to 96 hours.

A series of buprenorphine ester derivatives is also described in U.S. Pat. No. 7,964,610, issued to Reckitt Benckiser Healthcare (UK) Limited. Buprenorphine was modified with dicarboxylic acids or esters. Then, these derivatives were used for the treatment of opiate abuse/dependence and for the treatment of moderate to severe pain.

There are a variety of sustained release designs for buprenorphine indicated for the treatment of opioid dependence and chronic pain. For example, Titan Pharmaceuticals, Inc. developed a subcutaneous implant product of buprenorphine hydrochloride, Probuphine®, using their novel drug delivery system, ProNeura™, which is made from a mixture of ethylene vinyl acetate (EVA) and drug substance. Probuphine® is administrated once every six months through surgical implantation and removed from patients after treatment by surgical procedures.

Camurus established a novel drug delivery system, FluidCrystal®, which is based on lipid liquid crystals that are composed of phosphatidyl choline and glycerol dioleate. The formulation disclosed in US Patent Application Publication No. 2013/0190341 is designed as a long-acting buprenorphine product to treat opioid dependence and chronic pain, and is administrated by subcutaneous injection weekly or monthly.

U.S. Patent Application Publication No. 2003/0152638, by Brookwood Pharmaceuticals, Inc., discloses an injectable slow-release microsphere formulation that comprises buprenorphine and poly(D,L-lactide). This formulation is able to treat heroin and alcohol abuse for a period of at least 28 days in a mammal.

U.S. Patent Application Publication No. 2014/0271869 (Oakwood Laboratories LLC) discloses a biodegradable formulation, which utilized their proprietary technology, Chroniject™. The platform is a polymer-based injectable microspheres system for drug delivery. The buprenorphine microspheres could be generated in higher drug load and claimed to achieve sustained release for at least one month to several months.

Indivior PLC (WO 2011/154724) developed a monthly depot, which employed Atrigel System to produce an injectable, flowable formulation for the treatment of opioid dependency. The composition includes a buprenorphine free base, biodegradable polymer, and a biocompatible solvent. The dissolved liquid could be injected and transformed in situ into a solid implant, providing 1-month and 3-month release profiles. In addition, suspension and solution designs are disclosed in WO 2011/154725 and WO 2015/136253, respectively. The suspension is composed of buprenorphine and polyethylene glycol polymer in aqueous conditions, providing a therapeutic period of between 7 and 30 days in dogs after a single intramuscular or subcutaneous injection. As for the disclosed solution, the composition consists of buprenorphine or a salt form thereof and a biocompatible organic solvent without a biodegradable polymer. After a single subcutaneous injection in beagle dogs, the formulation is able to provide at least a one-month therapeutic period.

Despite the fact that the prior pharmaceutical preparations described above are able to provide buprenorphine with extended release, there is still a need for formulation with better characteristics, such as a formulation without an organic solvent to diminish the risks of local site irritation, or a formulation having higher bioavailability, or a pharmacokinetic profile with smaller fluctuation and without a significant burst effect after one single injection.

SUMMARY

The present disclosure relates to various sustained-release pharmaceutical compositions of buprenorphine, or a prodrug, a pharmaceutically acceptable salt, and a metabolite thereof, including aqueous suspension of buprenorphine derivatives, and controlled release matrix, such as aqueous suspension of microspheres, poly(lactic-co-glycolic acid (PLGA)-based solutions, lipid-based formulations, and sucrose acetate isobutyrate-based formulations. The formulations of the present disclosure perform a therapeutically effective duration of at least one week to several months.

One aspect of the present disclosure relates to injectable suspension or the combination thereof, without utilizing an organic solvent. It is known that utilizing organic solvents in parenteral pharmaceutical preparations would enhance solubility, whereas the risks of local site irritation would inevitably increase. An injectable pharmaceutical composition in accordance with one embodiment of the present disclosure includes a suspension of crystalline 3-acyl-buprenorphine, or a pharmaceutically acceptable salt thereof, in a diluent comprising polyethylene glycol (PEG) polymer, polysorbate, and phosphate buffer saline, wherein the injectable pharmaceutical composition exhibits a steady release profile over a period of at least one week and a minimal risk of local site irritation following a single injection.

In accordance with embodiments of the present disclosure, long-acting suspension formulations are prepared from crystalline 3-acyl-buprenorphine derivatives. The acyl group is an alkylcarbonyl group. An alkyl portion of the alkylcarbonyl group is a straight-chain, or a branched-chain, having 1 to 17 carbon atoms.

In one embodiment, the present disclosure provides crystalline 3-acyl-buprenoprhine derivatives having x-ray powder diffraction patterns as follows:

3-Acyl-buprenoprhine derivatives X-ray diffraction pattern (degrees 2θ) Buprenorphine acetate 4.70, 8.44, 9.38, 10.74, 12.42, 14.12, 17.72, 18.40, 18.78, 20.08, 20.56, 25.04, 26.88, 28.42, 28.46 Buprenorphine pivalate 5.93, 6.03, 9.08, 9.18, 9.33, 9.58, 9.68, 10.83, 10.93, 11.03, 12.18, 12.28, 12.78, 12.88, 12.98, 15.58, 15.73, 15.83, 15.98, 17.38, 17.53, 18.18, 18.28, 18.38, 19.43, 27.73, 27.83, 29.18 Buprenorphine pentanoate 2.33, 5.73, 5.83, 5.98, 6.13, 9.33, 9.43, 9.53, 9.63, 9.98, 10.08, 10.18, 11.83, 11.93, 12.03, 12.53, 12.68, 12.83, 12.98, 13.08, 15.73, 15.88, 16.03, 16.38, 18.28, 18.38, 18.58, 19.28, 19.43, 22.23 Buprenorphine hexanoate 2.33, 7.53, 8.13, 9.05, 10.93, 11.08, 12.93, 13.13, 13.38, 13.48, 15.88, 16.03, 17.18, 17.28, 17.73, 17.93, 21.13, 21.23, 21.33 Buprenorphine decanoate 5.80, 8.00, 10.50, 11.50, 11.60, 13.82, 14.44, 14.96, 16.06, 17.34, 18.32, 18.58, 18.98, 19.44, 20.92, 23.06, 23.40, 24.22, 24.38, 24.92 Buprenorphine dodecanoate 5.68, 8.03, 9.88, 9.98, 10.93, 11.38, 11.48, 17.13, 17.23, 17.33, 18.18, 18.28, 18.38, 18.93, 19.13, 19.23, 19.53, 21.03

In accordance with embodiments of the present disclosure, it relates to aqueous suspension, wherein the 3-acyl-buprenorphine, or a pharmaceutically acceptable salt thereof, is present at a concentration of 1-99% w/v, 5-90% w/v, 5-60% w/v, or 10-30% w/v.

In accordance with embodiments of the present disclosure, it relates to controlled release matrix formulations. The biocompatible organic solvent utilized in PLGA-based formulations, lipid-based formulations, and sucrose acetate isobutyrate-based formulations is N-methyl-2-pyrrolidone, ethyl acetate, ethanol, butanol, 2-butanol, isobutanol, isopropanol, glycerin, benzyl benzoate, dimethyl sulfoxide, N,N-dimethylacetamide, propylene glycol, dimethyl glycol, benzyl alcohol, an ester, an ether, an amide, a carbonate, a lactam, a sulfonyl, or any combination thereof.

In accordance with embodiments of the present disclosure, an injectable pharmaceutical composition may further comprise a preservative. In accordance with embodiments of the present disclosure, the preservative is selected from the group consisting of methylparaben, propylparaben and benzylalcohol.

In accordance with embodiments of the present disclosure, an injectable pharmaceutical composition is formulated for subcutaneous, intramuscular or intradermal injection.

Another aspect of the present disclosure relates to methods for treating opioid addiction, pain, or depression. A method in accordance with one embodiment of the present disclosure comprises administering to a subject in need thereof a therapeutically effective amount of the injectable pharmaceutical composition according to any embodiments described above.

In accordance with embodiments of the present disclosure, the administering is performed at a frequency of once per week, once per month, or once every three months.

Other aspects of the present disclosure will become apparent with the attached drawings and the following detailed descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the X-ray powder diffraction pattern of buprenorphine acetate crystal form.

FIG. 2 illustrates the differential scanning calorimetry (DSC) pattern of buprenorphine acetate crystal form.

FIG. 3 illustrates the ¹H nuclear magnetic resonance (NMR) spectrum of buprenorphine acetate crystal form.

FIG. 4 illustrates the Fourier-transform infrared spectroscopy (FTIR) spectrum of buprenorphine acetate crystal form.

FIG. 5 illustrates the X-ray powder diffraction pattern of buprenorphine pivalate crystal form.

FIG. 6 illustrates the DSC pattern of buprenorphine pivalate crystal form.

FIG. 7 illustrates the ¹H NMR spectrum of buprenorphine pivalate crystal form.

FIG. 8 illustrates the FTIR spectrum of buprenorphine pivalate crystal form.

FIG. 9 illustrates the X-ray powder diffraction pattern of buprenorphine pentanoate crystal form.

FIG. 10 illustrates the DSC pattern of buprenorphine pentanoate crystal form.

FIG. 11 illustrates the ¹H NMR spectrum of buprenorphine pentanoate crystal form.

FIG. 12 illustrates the FTIR spectrum of buprenorphine pentanoate crystal form.

FIG. 13 illustrates the X-ray powder diffraction pattern of buprenorphine hexanoate crystal form.

FIG. 14 illustrates the DSC pattern of buprenorphine hexanoate crystal form.

FIG. 15 illustrates the ¹H NMR spectrum of buprenorphine hexanoate crystal form.

FIG. 16 illustrates the FTIR spectrum of buprenorphine hexanoate crystal form.

FIG. 17 illustrates the X-ray powder diffraction pattern of buprenorphine decanoate crystal form.

FIG. 18 illustrates the DSC pattern of buprenorphine decanoate crystal form.

FIG. 19 illustrates the ¹H NMR spectrum of buprenorphine decanoate crystal form.

FIG. 20 illustrates the FTIR spectrum of buprenorphine decanoate crystal form.

FIG. 21 illustrates the X-ray powder diffraction pattern of buprenorphine dodecanoate crystal form.

FIG. 22 illustrates the DSC pattern of buprenorphine dodecanoate crystal form.

FIG. 23 illustrates the ¹H NMR spectrum of buprenorphine dodecanoate crystal form.

FIG. 24 illustrates the FTIR spectrum of buprenorphine dodecanoate crystal form.

FIG. 25 illustrates the in vitro dissolution % release of AS01-07.

FIG. 26 illustrates the in vitro dissolution % release of AS08-09.

FIG. 27 illustrates the in vitro dissolution % release of MSA02 and MSA05.

FIG. 28 illustrates the in vitro dissolution % release of MSB01-05.

FIG. 29 illustrates the in vitro dissolution % release of PS01, PS02, PS09, and PS10.

FIG. 30 illustrates the in vitro dissolution % release of PS03-08.

FIG. 31 illustrates the in vitro dissolution % release of BDSB1 and LS01-04.

FIG. 32 illustrates the pharmacokinetic (PK) profile of AS01-04 in rats.

FIG. 33 illustrates the PK profile of AS05-07 in rats.

FIG. 34 illustrates the PK profile of AS08 in minipigs.

FIG. 35 illustrates the PK profile of MSA02-05 and MSB01-02 in rats.

FIG. 36 illustrates the PK profile of MSA01, MSA02, and MSA05 in dogs.

FIG. 37 illustrates the PK profile of PS03 and PS10 in rats.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to formulations of buprenorphine derivatives in the forms of aqueous suspension of crystalline buprenorphine derivatives, aqueous suspension of microspheres, PLGA-based solutions, lipid-based formulations, and sucrose acetate isobutyrate-based formulations, having long-lasting release profiles after single dose administration and displaying minimal initial bursts for the treatment of opioid addiction, pain or depression. In accordance with embodiments of the present disclosure, the buprenorphine derivatives are 3-alkyl ester derivatives, i.e., esters formed between the 3-hydroxy (phenol) group of buprenorphine and alkylcarbonylation (acylation) reagents.

In accordance with embodiments of the present disclosure, an alkylcarbonyl reagent (R—CO—X), wherein R is an alkyl residue, may be an acyl chloride, an acyl anhydride, or an acyl active ester. The alkyl portion of an alkylcarbonyl group may be a straight-chain or branched alkyl group. The alkyl portion may contain any suitable number of carbons, such as 1-18 (C₁-C₁₈), 1-16 (C₁-C₁₆), 1-12 (C₁-C₁₂), 1-10 (C₁-C₁₀), 1-5 (C₁-C₅), or 1-3 (C₁-C₃). Examples of alkylcarbonyl (acyl) groups may include acetyl, propionyl, butyryl, pentanyl, hexanyl, decanyl, stearyl, and palmityl.

In accordance with embodiments of the present disclosure, the buprenorphine derivatives may be synthesized using conventional methods. Buprenorphine or its salt can be purchased from several commercial sources, such as Sigma-Aldrich. To prepare a buprenorphine derivative, buprenorphine (or its salt) may be reacted with an acyl chloride in the presence of a base (e.g., triethylamine) to form an ester bond. The product (3-acyl-buprenorphine or 3-alkylcarbonyl-buprenorphine) may be purified with conventional methods (e.g., column chromatography).

As used in this description, a buprenorphine derivative refers to 3-acyl-buprenorphine (3-alkylcarbonyl-buprenorphine) or a salt thereof. A buprenorphine derivative of the present disclosure may function as a prodrug, which may be converted into the parent compound, buprenorphine.

The crystalline buprenorphine derivatives were further characterized by X-ray diffraction (XRD), differential scanning calorimeters (DSC), nuclear magnetic resonance spectroscopy (NMR), and infrared spectroscopy (IR).

A formulation of the present disclosure may comprise a 3-acyl-buprenorphine derivative suspended in an aqueous diluent containing PEG polymer, polysorbate, and phosphate buffer saline. The aqueous suspended formulation may contain the buprenorphine derivative or a salt thereof in any suitable concentration, such as 1-99% w/v, 1-90% w/v, 5-90% w/v, 5-80% w/v, 10-70% w/v, or 10-60% w/v. It is noted that when a numerical range is disclosed in this description, it is intended to include all numbers within the ranges, as if each of these numbers have been individually disclosed.

A formulation of the present disclosure may further comprise another pharmaceutically acceptable excipient, carrier, diluent, or preservative. In accordance with embodiments of the present disclosure, a preservative may be selected from the group consisting of methylparaben, propylparaben and benzylalcohol.

A formulation of the present disclosure may comprise of microspheres of 3-acyl-buprenorphine derivative or a salt form thereof and an aqueous diluent containing phosphate-buffered saline, sodium carboxymethylcellulose, and polysorbate. The thermoplastic polymer utilized for microspheres may be a polylactide, a polyglycolide, a 50/50, 55/45, 60/40, 65/35, 70/30, 75/25, 80/20, 85/15, 90/10 or 95/5 poly(DL-lactic-co-glycolide) with a carboxyl terminal group or an ester terminated group or a combination thereof.

A formulation of the present disclosure may comprise of 3-acyl-buprenorphine derivative or a salt form thereof, thermoplastic polymer, and one or more suitable biocompatible solvents. The buprenorphine derivative may be in the form of a free base or a pharmaceutically acceptable salt thereof, such as a salt of HCL, formate, acetate, citric acid or the like. The thermoplastic polymer may be a polylactide, a polyglycolide, a 50/50, 55/45, 60/40, 65/35, 70/30, 75/25, 80/20, 85/15, 90/10 or 95/5 poly(DL-lactic-co-glycolide) with a carboxyl terminal group or an ester terminated group or a combination thereof. The biocompatible solvents may be organic solvents, such as N-methyl-2-pyrrolidone (NMP), ethyl acetate (EtOAc), ethanol (EtOH), butanol, 2-butanol, isobutanol, glycerin, benzyl benzoate (BnBzO), dimethyl sulfoxide, propylene glycol, dimethyl glycol, and benzyl alcohol.

A formulation of the present disclosure may comprise 3-acyl-buprenorphine derivative or a salt form thereof dissolved in a lipid-based solution comprising lecithin, diolein and biocompatible solvents. The biocompatible solvents may be organic solvents, such as N-methyl-2-pyrrolidone (NMP), ethyl acetate (EtOAc), ethanol (EtOH), butanol, 2-butanol, isobutanol, glycerin, benzyl benzoate (BnBzO), dimethyl sulfoxide, propylene glycol, dimethyl glycol, and benzyl alcohol.

A formulation of the present disclosure may comprise an ionic complex of 3-acyl-buprenorphine derivative or a salt form thereof, sucrose acetate isobutyrate (SAIB) dissolved or suspended in a biocompatible solvent. The biocompatible solvents may be organic solvents, such as N-methyl-2-pyrrolidone (NMP), ethyl acetate (EtOAc), ethanol (EtOH), butanol, 2-butanol, isobutanol, glycerin, benzyl benzoate (BnBzO), dimethyl sulfoxide, propylene glycol, dimethyl glycol, and benzyl alcohol.

The various formulations of the present disclosure do not have undesirable initial burst and may display a sustained releasing profile over 1 week, 2 weeks, 3 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months or longer. The formulations without the significant burst release of buprenorphine may not only reduce the risks of several systemic adverse effects, e.g., pinpoint pupils, sedation, hypotension, and respiratory depression, but also lessen the burden of physicians to monitor patients frequently. Furthermore, the aqueous suspension formulation of the buprenorphine derivative without an organic solvent exhibits high bioavailability, pharmaceutically effective plasma concentration for at least one week, and minimal risk of local site reactions.

Embodiments of the present disclosure will be further illustrated with the following examples. However, one skilled in the art would appreciate that these examples are for illustration only and that other modifications and variations are possible without departing from the scope of the disclosure.

Example 1: Synthesis of 3-acyl-buprenorphine Derivatives

The following description is the procedure for synthesis of 3-acyl-buprenorphine derivatives. To a suitable 3-necked round bottom flask, buprenorphine HCl and dichloromethane (DCM) were added for a suspension, which was placed in an ice bath for cooling. Afterwards, trimethylamine (TEA) was added slowly with stirring. Acyl chloride was then added dropwise into the flask. The ice bath was revoked after all the materials were added. The reaction mixture was carried out at ambient temperature for 1 to 4 hours. The reaction mixture was neutralized with saturated sodium bicarbonate aqueous solution. The organic layer was washed with brine and then dried with sodium sulfate. After condensation under reduced pressure, the crude buprenorphine derivative was obtained. (Table 1)

TABLE 1 Synthesis condition of various 3-acyl-buprenorphine derivatives Buprenorphine Entry HCl Acyl chloride Base Solvent 1-1 20.00 g, Acetyl chloride TEA DCM (200 mL) 39.7 mmol (3.74 g, 47.6 mmol) (8.03 g, 79.3 mmol) 1-2 1.00 g, Trimethylacetyl chloride TEA DCM (10 mL) 1.98 mmol (0.29 mL, 2.38 mmol) (0.4 g, 3.96 mmol) 1-3 1.00 g, Valeroyl chloride TEA DCM (10 mL) 1.98 mmol (0.28 mL, 2.38 mmol) (0.4 g, 3.96 mmol) 1-4 2.0 g, Hexanoyl chloride TEA DCM (20 mL) 3.97 mmol (0.64 g, 4.76 mmol) (0.8 g, 7.93 mmol) 1-5 10.00 g, Decanoyl chloride TEA DCM (100 mL) 19.84 mmol (4.54 g, 23.8 mmol) (5.53 mL, 39.68 mmol) 1-6 1.00 g, Dodecanoyl chloride TEA DCM (10 mL) 1.98 mmol (0.52 g, 2.38 mmol) (0.4 g, 3.95 mmol)

Example 2: Crystallization of 3-acyl-buprenorphine Derivatives

Following is the crystallization procedure of 3-acyl-buprenorphine derivatives. The crude 3-acyl-buprenorphine derivatives were dissolved in the solvents described in Table 2 at ambient temperature or heated oil or eater bath. Then, the dissolved mixtures were cooled with ice bath to form crystalline 3-acyl-buprenorphine derivatives.

TABLE 2 Crystallization condition of 3-acyl-buprenorphine derivatives Entry Crude Compound Solvent composition Temperature 2-1 Buprenorphine acetate, Ethanol 60° C. water bath to dissolve, gradually   9.6 g (95%, 90 mL) cooled to ambient temperature 2-2 Buprenorphine decanoate, Anhydrous ethanol 51° C. oil bath to dissolve, gradually 17.51 g (99.5%, 260 mL) cooled to ambient temperature 2-3 Buprenorphine decanoate, Ethanol 56° C. oil bath to dissolve, gradually 12.35 g (95%, 100 mL) cooled to ambient temperature 2-4 Buprenorphine decanoate, Isopropanol 59° C. water bath to dissolve, gradually   1.0 g (10 mL) cooled to ambient temperature 2-5 Buprenorphine decanoate, N-methyl-2-pyrrolidone 53° C. water bath to dissolve, cooled with   1.0 g (NMP, 3 mL) ice bath 2-6 Buprenorphine decanoate, Acetonitrile 58° C. water bath to dissolve, gradually   0.5 g (ACN, 7.5 mL) cooled to ambient temperature 2-7 Buprenorphine pivalate, Ethanol 60° C. water bath to dissolve, cooled with  1.15 g (95%, 11 mL) ice bath 2-8 Buprenorphine pentanoate, Ethanol 60° C. water bath to dissolve, cooled with   1.2 g (95%, 12 mL) ice bath 2-9 Buprenorphine hexanoate, Ethanol Dissolved at ambient temperature,   1.7 g (95%, 17 mL) cooled with ice bath 2-10 Buprenorphine dodecanoate, Ethanol 60° C. water bath to dissolve, cooled with  1.38 g (95%, 13.8 mL) ice bath

The crystalline 3-acyl-buprenorphine derivatives obtained were characterized by XRD, DSC, NMR and IR.

The crystal form of buprenorphine acetate was characterized by X-ray diffraction pattern (Bruker, D8 DISCOVER SSS Multipurpose Thin-film X-ray Diffractometer) having peaks at 4.70, 8.44, 9.38, 10.74, 12.42, 14.12, 17.72, 18.40, 18.78, 20.08, 20.56, 25.04, 26.88, 28.42, 28.46 degrees 2θ (FIG. 1 ), and its melting point was determined to be 167.69° C. by differential scanning calorimetry, DSC (Mettler-Toledo, TGA/DSC 3+STARe System) (FIG. 2 ). The structure of the buprenorphine acetate crystal form was confirmed with Nuclear Magnetic Resonance, NMR (Bruker, Ascend™ 400 MHz) and Fourier Transform Infrared Spectroscopy, FTIR (Thermo, Nicolet-IS10 Mattson Satellite-5000 spectrometer) (FIGS. 3 and 4 ). Representative ¹H NMR (400 MHz, CDCl₃): 6.81 (d, 1H, J=8.4 Hz), 6.62 (d, 1H, J=8.0 Hz), 5.93 (s, 1H), 4.45 (s, 1H), 3.49 (s, 3H), 3.03 (m, 2H), 2.94-2.81 (m, 1H), 2.64 (dd, 1H, J=4.8, 12.0 Hz), 2.40-2.24 (m, 7H), 2.14 (t, 1H, J=10.0 Hz), 2.04-1.78 (m, 3H), 1.77-1.68 (dd, 1H, J=2.8, 13.2 Hz), 1.42-1.38 (m, 4H), 1.15-1.01 (m, 10H), 0.89-0.77 (m, 1H), 0.77-0.65 (m, 1H), 0.51 (m, 2H), 0.14 (m, 2H). FTIR absorption band (cm⁻¹): 3439, 2928, 1760, 1610, 1450, 1399, 1192, 1136, 1094, 963, 827, 668 (±1 cm⁻¹).

The crystal form of buprenorphine pivalate was characterized by X-ray diffraction pattern (PHILIPS X'PERT Pro, PHILIPS X'PERT Pro MPD) having peaks at 5.93, 6.03, 9.08, 9.18, 9.33, 9.58, 9.68, 10.83, 10.93, 11.03, 12.18, 12.28, 12.78, 12.88, 12.98, 15.58, 15.73, 15.83, 15.98, 17.38, 17.53, 18.18, 18.28, 18.38, 19.43, 27.73, 27.83, 29.18 degrees 2θ (FIG. 5 ), and its melting point was determined to be 145.43° C. by means of differential scanning calorimetry, DSC (Mettler-Toledo, TGA/DSC 3+STARe System) (FIG. 6 ). The structure of the buprenorphine pivalate crystal form was identified with Nuclear Magnetic Resonance, NMR (Bruker, Ascend™ 400 MHz) and Fourier Transform Infrared Spectroscopy, FTIR (Thermo, Nicolet-IS10 Mattson Satellite-5000 spectrometer). (FIGS. 7 and 8 ). Representative ¹H NMR (400 MHz, CDCl₃): 6.78 (d, 1H, J=8.0 Hz), 6.61 (d, 1H, J=8.0 Hz), 5.94 (s, 1H), 4.44 (d, 1H, J=1.6 Hz), 3.48 (s, 3H), 3.04 (m, 2H), 2.91 (m, 1H), 2.64 (dd, 1H, J=4.8, 12.0 Hz), 2.42-2.20 (m, 4H), 2.13 (t, 1H, J=10.0 Hz), 2.05-1.89 (m, 2H), 1.89-1.68 (m, 2H), 1.37 (s, 3H), 1.34 (m, 10H), 1.06 (m, 10H), 0.82 (m, 1H), 0.69 (m, 1H), 0.51 (m, 2H), 0.14 (m, 2H). FTIR absorption band (cm⁻¹): 3428, 2954, 2827, 1753, 1614, 1478, 1448, 1407 (±1 cm⁻¹).

The crystal form of buprenorphine pentanoate was characterized by X-ray diffraction pattern (PHILIPS X'PERT Pro, PHILIPS X'PERT Pro MPD) having peaks at 2.33, 5.73, 5.83, 5.98, 6.13, 9.33, 9.43, 9.53, 9.63, 9.98, 10.08, 10.18, 11.83, 11.93, 12.03, 12.53, 12.68, 12.83, 12.98, 13.08, 15.73, 15.88, 16.03, 16.38, 18.28, 18.38, 18.58, 19.28, 19.43, 22.23 degrees 2θ (FIG. 9 ), and its melting point was determined to be 104.98 to 108.32° C. by means of differential scanning calorimetry, DSC (Mettler-Toledo, TGA/DSC 3+STARe System) (FIG. 10 ). The structure of the buprenorphine pentanoate crystal form was identified with Nuclear Magnetic Resonance, NMR (Bruker, Ascend™ 400 MHz) and Fourier Transform Infrared Spectroscopy, FTIR (Thermo, Nicolet-IS10 Mattson Satellite-5000 spectrometer) (FIGS. 11 and 12 ). Representative ¹H NMR (400 MHz, CDCl₃): 6.79 (d, 1H, J=8.0 Hz), 6.61 (d, 1H, J=8.0 Hz), 5.93 (s, 1H), 4.44 (d, 1H, J=1.6 Hz), 3.48 (s, 3H), 3.04 (m, 2H), 2.91 (m, 1H), 2.64 (dd, 1H, J=4.8, 12.0 Hz), 2.55 (t, 2H, J=7.6 Hz), 2.40-2.20 (m, 4H), 2.14 (t, 1H), 2.07-1.78 (m, 3H), 1.78-1.68 (m, 3H), 1.48-1.28 (m, 6H), 1.15-1.01 (m, 10H), 0.94 (t, 3H, J=7.2 Hz), 0.83 (m, 1H), 0.71 (m, 1H), 0.51 (m, 2H), 0.14 (m, 2H). FTIR absorption band (cm⁻¹): 3438, 2950, 2926, 2816, 1760, 1607, 1492, 1447, 1401 (±1 cm⁻¹).

The crystal form of buprenorphine hexanoate was characterized by X-ray diffraction pattern (PHILIPS X'PERT Pro, PHILIPS X'PERT Pro MPD) having peaks at 2.33, 7.53, 8.13, 9.05, 10.93, 11.08, 12.93, 13.13, 13.38, 13.48, 15.88, 16.03, 17.18, 17.28, 17.73, 17.93, 21.13, 21.23, 21.33 degrees 2θ (FIG. 13 ), and its melting point was determined to be 80.30 to 84.31° C. by means of differential scanning calorimetry, DSC (Mettler-Toledo, TGA/DSC 3+STARe System) (FIG. 14 ). The structure of the buprenorphine hexanoate crystal form was identified with Nuclear Magnetic Resonance, NMR (Bruker, Ascend™ 400 MHz) and Fourier Transform Infrared Spectroscopy, FTIR (Thermo, Nicolet-IS10 Mattson Satellite-5000 spectrometer) (FIGS. 15 and 16 ). Representative ¹H NMR (400 MHz, CDCl₃): 6.79 (d, 1H, J=8.0 Hz), 6.61 (d, 1H, J=8.0 Hz), 5.93 (s, 1H), 4.44 (d, 1H, J=1.6 Hz), 3.48 (s, 3H), 3.04 (m, 2H), 2.91 (m, 1H), 2.64 (dd, 1H, J=4.8, 12.0 Hz), 2.54 (t, 2H, J=7.6 Hz), 2.45-2.20 (m, 4H), 2.14 (t, 1H), 2.08-1.65 (m, 6H), 1.42-1.30 (m, 8H), 1.16-1.02 (m, 10H), 0.93 (t, 3H, J=6.8 Hz), 0.83 (m, 1H), 0.71 (m, 1H), 0.51 (m, 2H), 0.14 (m, 2H). FTIR absorption band (cm⁻¹): 3453, 2944, 2923, 2865, 1760, 1610, 1449, 1398 (±1 cm⁻¹).

The crystal form of buprenorphine decanoate was characterized with X-ray diffraction pattern (Bruker, D8 DISCOVER SSS Multipurpose Thin-film X-ray Diffractometer), which shows peaks at 5.80, 8.00, 10.50, 11.50, 11.60, 13.82, 14.44, 14.96, 16.06, 17.34, 18.32, 18.58, 18.98, 19.44, 20.92, 23.06, 23.40, 24.22, 24.38, 24.92 degrees 2θ (FIG. 17 ), and its melting point of the crystal product was determined to be 86.37° C. by means of differential scanning calorimetry, DSC (Mettler-Toledo, TGA/DSC 3+STARe System) (FIG. 18 ). The structure of buprenorphine decanoate was identified with Nuclear Magnetic Resonance, NMR (Bruker, Ascend™ 400 MHz) and Fourier Transform Infrared Spectroscopy, FTIR (Thermo, Nicolet-IS10 Mattson Satellite-5000 spectrometer). (FIGS. 19 and 20 ). Representative ¹H NMR (400 MHz, CDCl₃): 6.79 (d, 1H, J=8.0 Hz), 6.61 (d, 1H, J=8.0 Hz), 5.94 (s, 1H), 4.44 (d, 1H, J=1.6 Hz), 3.48 (s, 3H), 3.04 (m, 2H), 2.91 (m, 1H), 2.64 (dd, 1H, J=5.2, 12.0 Hz), 2.54 (t, 2H, J=7.2 Hz), 2.40-2.25 (m, 4H), 2.14 (t, 1H, J=9.6 Hz), 2.03-1.90 (m, 2H), 1.87-1.80 (m, 1H), 1.75-1.68 (m, 3H), 1.42-1.29 (m, 17H), 1.12-1.06 (m, 9H), 0.94 (t, 3H, J=6.8 Hz), 0.83 (m, 1H), 0.71 (m, 1H), 0.51 (m, 2H), 0.14 (m, 2H). FTIR absorption band (cm⁻¹): 3439, 2928, 1760, 1610, 1450, 1399, 1192, 1136, 1094, 963, 827, and 668 (±1 cm⁻¹).

The crystal form of buprenorphine dodecanoate was characterized by X-ray diffraction pattern (PHILIPS X'PERT Pro, PHILIPS X'PERT Pro MPD) having peaks at 5.68, 8.03, 9.88, 9.98, 10.93, 11.38, 11.48, 17.13, 17.23, 17.33, 18.18, 18.28, 18.38, 18.93, 19.13, 19.23, 19.53, 21.03 degrees 2θ (FIG. 21 ) and its melting point was determined to be 74.99 to 77.30° C. by means of differential scanning calorimetry, DSC (Mettler-Toledo, TGA/DSC 3+STARe System) (FIG. 22 ). The structure of the buprenorphine dodecanoate crystal form was identified with Nuclear Magnetic Resonance, NMR (Bruker, Ascend™ 400 MHz) and Fourier Transform Infrared Spectroscopy, FTIR (Thermo, Nicolet-IS10 Mattson Satellite-5000 spectrometer) (FIGS. 23 and 24 ). Representative ¹H NMR (400 MHz, CDCl₃): 6.79 (d, 1H, J=8.0 Hz), 6.61 (d, 1H, J=8.0 Hz), 5.94 (s, 1H), 4.44 (d, 1H, J=2.0 Hz), 3.48 (s, 3H), 3.10-3.00 (m, 2H), 2.97-2.87 (m, 1H), 2.64 (dd, 1H, J=4.8, 12.0 Hz), 2.54 (t, 2H, J=7.6 Hz), 2.42-2.22 (m, 4H), 2.14 (t, 1H, J=9.6 Hz), 2.07-1.78 (m, 3H), 1.77-1.66 (m, 3H), 1.46-1.22 (m, 20H), 1.14-1.01 (m, 10H), 0.90 (t, 3H, J=6.8 Hz), 0.87-0.78 (m, 1H), 0.77-0.65 (m, 1H), 0.58-0.45 (m, 2H), 0.19-0.08 (m, 2H). FTIR absorption band (cm⁻¹): 3453, 2944, 2923, 2865, 1760, 1610, 1449, 1398 (±1 cm⁻¹).

The above examples show limited numbers of ester derivatives of the disclosure. One skilled in the art would appreciate that other similar ester derivatives may be prepared in similar manners.

Example 3: Solubility of Buprenorphine Derivatives and Salt Form Thereof in Dissolution Medium

Excess amount of compounds, including buprenorphine free base, buprenorphine derivatives, or salt form thereof were weighed into a glass tube containing 5 mL dissolution medium. The medium was the same as in previous examples. The tube was then sealed and placed into a reciprocal shaker at the rate of 60 rpm in a 55° C. water bath. The solution was filtered with 0.45 μm Nylon filter. Afterwards, the filtrate was further diluted with acetonitrile. The content of each compound was measured with the HPLC method.

TABLE 3 Solubility of buprenorphine derivatives Compound Solubility (mg/mL) Buprenorphine free base 1.176 Buprenorphine acetate (crystal form) 0.697 Buprenorphine pentanoate (crystal form) 0.498 Buprenorphine hexanoate (crystal form) 0.670 Buprenorphine pivalate (crystal form) 0.160 Buprenorphine decanoate (crystal form) 0.112 Buprenorphine dodecaonate (crystal form) 0.269 Buprenorphine palmitate 0.027 Buprenorphine stearate 0.020

TABLE 4 Solubility of salt forms of buprenorphine derivatives Compound Solubility (mg/mL) Buprenorphine-pamoic acid salt 2.095 Buprenorphine acetate-citric acid salt 1.377 Buprenorphine acetate-maleic acid salt 1.481 Buprenorphine acetate-hydrochloride salt 1.716 Buprenorphine acetate-pantoic acid salt 1.546 Buprenorphine decanoate-citric acid salt 2.696 Burpenorphine decaonate-L-tartaric acid salt 1.507 Buprenorphine stearate-citric acid salt 2.452 Buprenorphine stearate-L-tartaric acid salt 3.504

Table 3 shows that the solubilities of the buprenorphine derivatives (in crystal form) were less than their parent compound (buprenorphine free base). The solubility of buprenorphine decanoate crystal form was nearly 10 times poorer than that of the parent compound. After preparation of the salt forms, the solubilities of salt forms of buprenorphine derivatives were found to be superior to their free base and parent compound (Table 4).

Example 4: Preparation of Aqueous Suspension of Buprenorphine Derivatives

Weighed known amount of 3-acyl-buprenorphine derivative and suspended it with diluent, which was composed of PEG4000 (30 mg/mL) and Tween 20 (3 to 6 mg/mL) in PBS buffer. Mixed the formulation by sonicating and shaking. The formulations were further milled. The composition and process were listed in Table 5. The particle size distribution results were shown in Table 6.

TABLE 5 Composition, milling process and administration route of buprenorphine derivatives aqueous suspension Administration Code Buprenorphine derivatives Milling Process route AS01 Buprenorphine decanoate, Agate mortar IM 10% w/v AS02 Buprenorphine decanoate, — IM 10% w/v AS03 Buprenorphine decanoate, — SC 10% w/v AS04 Buprenorphine decanoate, — IM 10% w/v AS05 Buprenorphine decanoate, Bead milling, 6 mm Iron beads SC 20% w/v AS06 Buprenorphine decanoate, Bead milling, 0.50 mm Zirconia SC 20% w/v Grinding Media AS07 Buprenorphine hexanoate, Bead milling, 2 mm glass beads SC 10% w/v AS08 Buprenorphine hexanoate, Bead milling, 0.50 mm Zirconia SC 20% w/v Grinding Media AS09 Buprenorphine hexanoate, High pressure homogenizers (6000 — 15% w/v rpm, 20000 psi) AS10 Buprenorphine hexanoate, Bead milling, 0.50 mm Zirconia — 30% w/v Grinding Media

TABLE 6 Particle size distributions of aqueous suspension of buprenorphine derivatives Volume Statistics Specific Surface Formulation d10 (μm) d50 (μm) d90 (μm) Area (cm²/g) AS01 2.15 17.07 62.33 10319 AS02/AS03 3.22 15.68 44.43 8816 AS08 8.90 11.33 36.83 4521 AS09 1.58 4.99 14.60 18183

Example 5: Preparation of Microspheres Method A

The process of microsphere preparation in Method A was carried out by double emulsion. A known amount of poly(lactide-co-glycolide) and active pharmaceutical ingredient were weighed into a glass vial. Dichloromethane (3 mL) was used to dissolve the mixture. Polyvinyl alcohol aqueous solution (1%, 6 mL) was added thereto. The mixture was suspended using a homogenizer at the rate of 5000 rpm for 5 minutes in an ice bath. The homogenous suspension was then dropped into a beaker containing polyvinyl alcohol aqueous solution (1%, 1000 mL) with stirring (800 rpm) at 40° C. under a heating condition. After 3 hours, the microparticles were collected with centrifuge and washed with dd-water several times sequentially. The residual water in microparticles was removed by freeze drying. The formulation compositions are listed in Table 7 below.

TABLE 7 Composition of microspheres (Method A) Particle API PLGA type (mean, μm) Formulation Compound wt % LA/GA ratio E.E. (%) size MSA01 Buprenorphine decanoate 40% 75/25 100.2 ± 1.5 24.6 ± 7.7 (iv 0.21, ester capped) MSA02 Buprenorphine decanoate citric 40% 50/50 108.9 ± 5.1 24.6 ± 7.9 acid salt (iv 0.30, acid terminated) MSA03 Buprenorphine decanoate citric 50% 50/50 115.9 ± 2.9  8.4 ± 6.3 acid salt (iv 0.21, acid   terminated)   MSA04 Buprenorphine decanoate citric 40% 50/50 115.6 ± 1.7  5.6 ± 6.2 acid salt (iv 0.21, acid terminated) MSA05 Buprenorphine decanoate citric 40% 75/25 111.0 ± 3.6 20.8 ± 7.2 acid salt (iv 0.21, ester capped)

Method B

Method B was conducted using a T-shaped loop (Western Analytical, Tee Asy Tefzel 1/16″ 0.020″ thru). The terminal inlet was inserted with one set of syringe and needle (Hamilton 81520 5 mL, Model 1005 TLL and Hamilton Metal Hub N726S NDL 6/PK (26S/2″/3)) as a dispersing phase part. One of the lateral inlets was connected with a pump with a tubing as a continuous phase part.

The microspheres were prepared using a continuous emulsification/solvent extraction procedure. The dispersing phase was filled into a syringe with an API-containing polymer solution, which was composed of PLGA and dichloromethane. The flow rate of the dispersing phase was controlled by an infusion syringe pump (KDS 100, KD Scientific) at a rate of 0.3 mL/min. At the same time, the continuous phase containing 1% polyvinyl alcohol aqueous solution was pumped at a rate of 2 mL/min. The outlet was connected to a beaker containing 1% polyvinyl alcohol aqueous solution through a tubing. The quenching process was carried out at ambient or heating condition. The microspheres were filtered with 0.45 μm membrane and washed with dd-water several times. Thereafter, the microspheres were dried in vacuum at ambient temperature. The formulation compositions are listed in Table 8.

TABLE 8 Composition of microsphere (Method B) PLGA type API I.V. Particle size Formulation Compound wt % LA/GA (dL/g) E.E. (mean, μm) MSB0 Buprenorphine decanoate 40% 75/25 0.7 101.6% NA MSB02 Buprenorphine hexanoate 40% 75/25 0.2 108.7% NA MSB03 Buprenorphine decanoate 40% 75/25 0.2 101.6 57.4 citric acid salt MSB04 Buprenorphine acetate 40% 75/25 0.2 101.2 30 MSB05 Buprenorphine dodecanoate 40% 75/25 0.2 106.8 25

Example 6: Preparation of PLGA-Based Formulation

The buprenorphine derivatives, poly(lactide-co-glycolide), and a biocompatible solvent were added into a glass vial. The mixture was placed into a 50° C. water bath with constant stirring until all the ingredients were dissolved. The mixture was removed from water bath, and the solution was generated at ambient temperature with stirring simultaneously. The compositions of the PLGA-based formulations are listed in Table 9 below.

TABLE 9 Compositions of PLGA-based formulations Formulation Buprenorphine derivatives, wt% PLGA type, wt% Solvent, wt % PS01 Buprenorphine decanoate, 20% 50/50 (17 kD, ester capped), 20% EtOAc, 60% PS02 Buprenorphine decanoate, 20% 75/25 (95 kD, ester capped), 20% EtOAc, 60% PS03 Buprenorphine decanoate, 30% 75/25 (17 kD, ester capped), 10% NMP, 60% PS04 Buprenorphine decanoate, 30% 75/25 (95 kD, ester capped), 10% NMP, 60% PS05 Buprenorphine decanoate, 30% Polylactide, (17 kD, ester capped), 10% NMP, 60% PS06 Buprenorphine decanoate, 30% Polylactide, (17 kD, acid terminated), NMP, 60% 10% PS07 Buprenorphine decanoate, 30% 50/50 (17 kD, ester capped), 10% NMP, 60% PS08 Buprenorphine decanoate, 30% 50/50 (44 kD, ester capped), 10% NMP, 60% PS09 Buprenorphine decanoate citric 75/25 (17 kD, ester capped), 20% EtOAc, 60% acid salt, 20% PS10 Buprenorphine hexanoate, 40% 75/25 (17 kD, ester capped), 10% EtOAc, 50%

Example 7: Preparation of Lipid-Based Formulations

The lipid-based formulations were prepared by mixing buprenorphine derivatives, lecithin, diolein, and a biocompatible solvent. The compositions of the lipid-based formulations are listed in Table 10 below.

TABLE 10 Compositions of lipid-based formulations Composition w/w Formulation Buprenorphine derivatives Lecithin Diolein Solvent LS01 Buprenorphine hexanoate, 35% 17.5% 17.5% N-Methyl-2-Pyrrolidone, 30% LS02 Buprenorphine hexanoate, 35% 17.5% 17.5% Benzyl benzoate, 30% LS03 Buprenorphine decanoate, 25%   20%   20% N-Methyl-2-Pyrrolidone, 35% LS04 Buprenorphine decanoate, 25%   20%   20% Benzyl benzoate, 35%

Example 8: Preparation of SAIB-Based Liquid Formulations

Buprenorphine decanoate (203.1 mg, 1.0 eq.) was dissolved in ethanol (2 mL). Sodium dodecyl sulfate (SDS) was dissolved in distilled deionized water (20 mL). The buprenorphine decanoate solution was added into the SDS solution dropwise and generated tiny precipitates in the mixture solution. The mixture was concentrated under reduced pressure to form buprenorphine decanoate-SDS ionic complex. The ionic complex (6% w/w) was further mixed with sucrose acetate isobutyrate (SAIB, 38% w/w) and NMP (56% w/w) to form formulation BDSB1.

Example 9. In Vitro Dissolution Test of Formulations

The formulations in examples 4-8 were further investigated for their in vitro dissolution profile. The dissolution medium composed of 1% sodium dodecyl sulfate and 0.02% sodium azide in phosphate buffered saline. The tubes were incubated in a reciprocal shaker at the rate of 60 rpm with 37° C. or 55° C. water bath simultaneously. The tubes were pulled, sampled as 1 mL solution, and then refilled with 1 mL fresh medium subsequently at specific timepoints. These samples were analyzed through HPLC for buprenorphine derivatives and their parent compound, i.e., buprenorphine free base. The in vitro releasing profiles are revealed in FIGS. 25 to 31 and Tables 11 to 18.

TABLE 11 In vitro dissolution % release of AS01-04 % Release at 55° C. Time (days) AS01 AS02 AS03 AS04 0 0.0 0.0 0.0 0.0 0.042 1.5 0.9 0.9 0.0 0.083 3.7 2.1 2.1 0.6 0.167 7.0 4.2 4.1 1.2 1 24.3 16.0 15.7 5.8 2 34.8 25.6 24.6 10.4 3 42.3 32.7 31.1 13.0 4 49.5 40.8 38.4 17.2 5 54.9 47.1 44.4 21.1 6 56.7 53.3 49.7 24.4 7 60.6 57.7 53.7 26.6 8 63.2 59.3 55.4 28.3 9 66.8 63.9 59.7 31.2 10 68.7 67.5 61.7 33.2 11 67.4 70.7 66.3 35.8 12 72.3 72.3 67.2 37.2 14 75.5 77.0 71.7 41.7 16 77.8 80.2 75.3 43.5 17 78.1 81.6 76.2 42.3 21 79.8 85.4 79.6 48.4 24 84.2 88.5 83.6 51.5 28 83.8 89.4 84.7 55.7 31 84.5 89.9 86.8 58.1 35 89.0 92.9 86.6 61.8

TABLE 12 In vitro dissolution % release of AS05-07 % Release at 55° C. Time Time (days) AS05 AS06 (days) AS07 0 0 0 0 0 0.042 7.6 9.3 0.042 58.00 0.083 11.8 15.0 0.167 90.67 0.167 18.1 24.9 1 102.33 1 42.0 61.1 2 103.92 2 49.4 75.3 5 101.94 5 60.8 82.0 — — 6 66.9 88.0 — —

TABLE 13 In vitro dissolution % release of AS08-09 % Release at 37° C. Time Time (hours) AS08 (hours) AS09 0 0.24 0 0.00 1 56.5 0.5 80.39 2 60.0 1 97.96 4 65.6 2 99.98 6 69.1 4 101.69 8 71.7 6 99.96 24 80.9 8 102.72 48 99.7 24 105.61

TABLE 14 In vitro dissolution % release of MSA02 and MSA05 % Release at 37° C. Time (days) MSA02 MSA05 0 0.00 0.00 1 7.35 10.02 7 12.90 12.40 14 20.54 13.58 21 36.11 14.75 28 53.02 15.23 35 78.19 15.87 42 89.62 16.35 49 95.97 16.92 56 97.28 18.38 63 — 25.50 70 — 48.79 77 — 64.91 84 — 71.65

TABLE 15 In vitro dissolution % release of MSB01-05 % Release at 55° C. Time Time Time Time Time (days) MSB01 (days) MSB02 (days) MSB03 (days) MSB04 (days) MSB05 0 0 0 0 0 0 0 0 0 0 0.042 12 0.042 6 0.042 1.3 0.042 19.1 0.042 3.4 0.083 12 0.083 8 0.083 2.3 0.083 23.1 0.083 3.5 0.167 14 0.146 11 0.167 3.9 0.167 26.4 0.146 3.7 1 20 1 30 1 13.1 1 45.8 1 4.9 2 25 2 46 2 19.9 2 56.6 3 10.0 3 29 3 55 3 26.7 3 59.5 7 18.5 4 33 6 67 4 36 5 70.6 8 18.0 7 46 9 68 5 40.5 6 70.5 9 19.7 8 50 13 68 6 44.5 7 71.9 10 22.7 9 55 21 68 8 48.5 8 74.2 11 26.4 10 58 27 70 10 58.1 9 75.3 15 33.5 11 63 — — 14 72.2 10 76.5 21 42.5 14 69 — — 21 95.4 13 73.4 28 55.3 17 70 — — 24 97.1 16 78.8 36 72.4 21 75 — — — — — — — — 24 77 — — — — — — — — 29 80 — — — — — — — — 35 83 — — — — — — — —

TABLE 16 In vitro dissolution % release of PS01, PS02, PS09, and PS10 % Release at 55° C. Time Time Time (days) PS01 PS02 (days) PS09 (days) PS10 0 0 0 0 0 0 0 0.042 15 6 0.042 20.7 0.042 0.7 0.083 20 10 0.083 29.5 0.083 1.1 0.167 25 15 0.167 39.4 0.167 2.6 1 54 34 1 55.5 1 5.3 2 75 48 2 60 4 18.1 3 87 57 3 62.1 7 25.4 4 95 66 4 64.5 13 34.9 5 102 71 5 66.9 15 38.7 6 — 75 — — 19 44.1 7 — 77 — — 27 58 8 — 79 — — — — 9 — 82 — — — — 10 — 84 — — — — 16 — 104 — — — —

TABLE 17 In vitro dissolution % release of PS03-08 % Release at 55° C. Time Time Time (days) PS03 (days) PS04 (days) PS05 PS06 PS07 PS08 0 0 0 0 0 0 0 0 0 0.042 2 0.042 1 0.042 0.9 0.9 0.7 0.4 0.083 2 0.083 1 0.083 1.2 1.4 1.1 0.4 0.167 2 1 5 0.167 2.1 2.4 2 0.8 1 8 2 9 1 10.1 8.7 8.9 2.9 2 12 7 27 2 18.7 14 15.2 5.1 3 17 9 31 3 26.6 19 21 7.4 5 25 12 43 5 37.8 26.7 28.6 11.8 6 28 13 46 6 42 30.1 31.7 14.2 7 32 15 50 7 45.9 33.4 34.8 16.6 8 36 19 59 8 48.7 36 37 19.2 9 40 22 62 9 51.7 39 39.4 21.8 14 65 26 64 12 58.6 46.7 47.5 27.6 19 85 29 69 19 68.2 58.5 60.6 37.8 22 91 35 75 26 75 69.3 73.3 46.4 26 95 37 73 33 76.4 74.6 80.1 52.1 — — 40 82 41 79 79.7 83.9 58.5 — — 43 84 47 79.4 81.8 83.8 62.4 — — 47 84 54 77.2 84.3 84.5 65 — — 50 86 — — — — — — — 54 87 — — — — — — — 57 85 — — — — — — — 61 88 — — — — — — — 65 90 — — — — —

TABLE 18 In vitro dissolution % release of BDSB1, LS01-04 % Release at 55° C. Time Time Time (days) BDSB1 (days) LS01 LS02 (days) LS03 LS04 0 0 0 0 0 0 0 0 0.042 1 0.063 1.98 0.00 0.125 5.48 0.50 0.083 1 0.208 5.12 3.40 0.271 8.58 1.75 0.167 2 1 19.7 6.85 1 15.5 4.82 1 3 2 28.9 7.10 2 23.8 9.16 2 5 3 35.4 7.75 5 50.6 12.1 6 13 6 60.0 9.85 8 70.6 14.5 7 16 10 75.3 21.9 12 88.2 17.4 8 17 13 84.1 24.6 15 94.8 19.7 10 20 16 87.1 26.0 20 100.7 21.8 14 26 20 89.7 29.2 — — — 22 32 24 99.2 32.2 — — — 27 35 28 — 33.8 — — — 35 42 — — — — — — 42 47 — — — — — — 48 50 — — — — — —

Example 10: Pharmacokinetic Profile of Aqueous Suspension of Buprenorphine Derivatives in Rats and Minipigs

The aqueous suspension formulations of buprenorphine derivatives in Example 4 were administered subcutaneously or intramuscularly in SD male rats at a dose of 60 mg/kg buprenorphine equivalent. The resulted mean plasma concentrations of buprenorphine versus time profiles were shown in FIGS. 32-33 and Tables 19-20. Formulation AS08 was injected in Lanyu male minipigs subcutaneously. The mean plasma concentrations of buprenorphine versus time profiles are shown in FIG. 34 and Table 21.

TABLE 19 Mean plasma concentrations of buprenorphine after injection in rats AS01 AS02 AS03 AS04 Time Mean S.D. Mean S.D. Mean S.D. Mean S.D. (days) (ng/mL) (n = 3) (ng/mL) (n = 3) (ng/mL) (n = 3) (ng/mL) (n = 3) 0 0.04 0.07 0.00 0.00 0.00 0.00 0.00 0.00 0.021 14.61 9.36 3.59 0.86 1.89 0.20 3.40 3.30 0.042 18.5 6.94 11.4 5.84 4.92 3.08 6.93 1.50 0.083 9.51 2.72 7.25 2.54 2.12 0.56 10.0 1.95 0.17 11.63 1.42 8.01 3.48 1.67 0.40 7.41 1.18 0.25 12.32 2.63 7.25 2.09 2.13 0.30 6.71 3.02 1 16.8 5.28 9.05 4.06 4.67 1.37 5.25 0.35 3 24.5 1.42 16.7 3.87 6.15 1.87 3.95 0.56 7 54.9 7.28 46.3 11.1 15.9 5.8 14.0 3.27 10 53.8 7.46 47.2 16.3 25.4 6.67 23.1 2.81 14 25.1 7.15 25.6 0.96 27.1 0.66 23.3 6.09 21 10.5 4.61 14.3 6.07 17.6 3.02 14.3 5.48 28 2.73 1.78 6.56 2.99 7.74 2.22 7.42 3.88 35 0.52 0.41 4.2 2.28 5.28 2.23 4.00 2.80 42 0.23 0.22 1.66 1.07 2.87 1.15 1.94 1.64 49 0.00 0.00 0.68 0.36 1.62 0.82 0.88 0.77 56 — — — — 1.41 0.54 — — 63 — — — — 1.17 0.40 — — 70 — — — — 0.89 0.47 — —

TABLE 20 Mean plasma concentrations of buprenorphine after injection in rats AS051 AS06 AS07 S.D. S.D. S.D. Time Mean (n = Mean (n = Time (n = Mean (days) (ng/mL) 3) (ng/mL) 3) (days) 3) (ng/mL) 0 3.26 0.07 2.02 2.39 0 0 0 0.042 3.04 1.82 3.09 2.77 0.083 1.72 0.63 0.083 2.73 1.55 3.27 1.93 0.167 2.82 0.65 0.25 3.59 2.64 3.84 2.85 0.25 3.54 0.68 1 5.11 3.13 5.30 3.36 1 6.69 2.68 2 4.83 3.10 6.54 2.70 2 6.18 1.48 3 5.01 2.76 6.40 2.65 3 6.78 2.13 4 6.79 4.10 6.15 1.42 7 2.92 0.92 7 10.5 4.69 13.1 1.88 10 1.21 0.75 10 8.73 3.32 11.0 3.05 14 0.27 0.23 14 7.25 4.72 7.78 2.97 — — — 17 4.90 3.41 4.07 3.35 — — —

TABLE 21 Mean plasma concentrations of buprenorphine after injection in minipig AS08 Time (days) Mean (ng/mL) S.D. (n = 3) 0 0.177 0.21 0.08 0.228 0.30 0.17 0.227 0.28 0.25 0.217 0.26 1 1.01 0.20 2 1.70 0.69 3 1.54 0.70 4 1.66 0.57 5 2.19 0.80 6 2.98 1.14 7 3.20 0.93 8 3.37 0.73 9 3.15 0.61 10 2.89 0.50 12 2.51 0.51 14 2.15 0.35 21 1.46 0.73

Example 11: Pharmacokinetic Profile of Aqueous Suspension of Microspheres Containing Buprenorphine Derivatives in Rats and Dogs

Four buprenorphine decanoate citric acid salt-containing microspheres formulations as shown in Example 5 were prepared as suspension at a concentration of 100 to 150 mg/mL. The diluent was composed of 10 mM phosphate-buffered saline, 1.25% sodium carboxymethylcellulose, and 0.05% Tween 80. The suspension formulations were intramuscularly or subcutaneously injected in SD male rats at dose of 60 mg/kg buprenorphine equivalent. The pharmacokinetic profile results are shown in FIG. 35 and Tables 22-23.

TABLE 22 Mean plasma buprenorphine levels after intramuscular injection of MSA02-05 in rats Time Mean S.D. Mean S.D. Mean S.D. Mean S.D. (days) (ng/mL) (n = 3) (ng/mL) (n = 3) (ng/mL) (n = 3) (ng/mL) (n = 3) 0 0.03 0.05 0.21 0.37 0.32 0.28 0.09 0.01 0.007 1.18 0.24 2.10 0.73 4.26 2.27 1.45 0.60 0.021 2.41 0.95 5.30 1.03 6.36 2.05 3.18 0.87 0.042 5.93 2.2 9.23 1.99 12.1 1.49 6.26 1.01 0.083 13.9 4.02 13.0 1.74 16.3 3.02 14.3 0.95 0.167 20.4 2.27 16.1 2.22 19.2 1.12 22.0 2.44 0.25 22.4 2.74 15.6 1.57 20.4 7.90 20.1 3.16 1 18.8 2.86 18.7 11.0 15.6 4.48 8.13 1.02 4 18.30 2.84 36.4 16.6 22.2 4.54 12.31 5.09 7 24.8 2.55 96.2 15.90 75.8 21.3 20.2 7.30 10 33.0 7.60 38.4 17.30 47.7 3.15 18.2 6.77 14 27.47 2.12 10.8 2.65 11.6 5.69 13.0 1.04 17 19.7 3.05 6.43 3.18 4.72 5.09 12.6 1.92 21 13.7 2.57 2.98 1.24 2.42 3.24 12.4 0.75 24 16.1 3.00 1.53 0.56 1.49 2.16 11.1 2.16 28 11.0 2.40 0.80 0.71 0.81 1.02 8.69 2.68 31 7.59 1.83 — — — — 7.74 2.46 35 3.62 0.93 — — — — 5.54 1.75 38 1.67 0.54 — — — — 5.77 2.26 42 0.49 0.46 — — — — 5.03 1.43 45 0.21 0.21 — — — — 4.70 1.47 49 — — — — — — 4.04 1.03 53 — — — — — — 3.98 1.23 56 — — — — — — 2.98 0.61 59 — — — — — — 3.55 1.55 63 — — — — — — 2.86 0.57 66 — — — — — — 2.52 0.77 70 — — — — — — 2.37 0.38 73 — — — — — — 2.20 0.70 77 — — — — — — 2.02 0.30 79 — — — — — — 1.90 0.39 84 — — — — — — 2.14 0.18 88 — — — — — — 1.71 0.43

TABLE 23 Mean plasma buprenorphine levels after subcutaneous injection of MSB01-02 in rats MSB01 MSB02 Time Mean S.D. Mean S.D. (days) (ng/mL) (n = 4) (ng/mL) (n = 4) 0 0.00 0.00 0.00 0.00 0.042 1.04 0.64 6.32 2.80 0.083 2.01 0.68 18.8 5.97 0.25 3.09 0.63 24.2 8.30 1 3.88 0.99 13.2 1.59 3 4.78 1.06 7.22 0.70 7 11.4 3.84 8.63 3.25 10 13.0 3.54 5.67 2.24 14 14.2 0.79 5.47 2.58 21 14.4 1.90 6.04 4.94 28 11.7 2.74 7.58 5.38 35 9.01 1.05 7.64 3.13 42 6.54 1.78 8.31 1.61 49 4.43 0.85 8.19 2.16 56 4.41 0.24 9.74 1.58 63 5.53 1.37 10.2 2.67 70 4.78 0.64 8.45 3.55 77 3.51 1.04 6.30 1.82 84 2.02 0.54 5.39 1.62

Three buprenorphine decanoate and citric acid salt thereof contained microspheres formulations as shown in Example 5 were prepared as suspension at the concentration of 300 mg/mL. The diluent was composed of 10 mM phosphate-buffered saline, 1.25% sodium carboxymethylcellulose, and 0.05% Tween 80. The suspension formulations were intramuscularly injected in beagle dogs at dose of 18.9 mg/kg buprenorphine equivalent. The pharmacokinetic profile results are shown in FIG. 36 and Table 24.

TABLE 24 Mean plasma buprenorphine levels after intramuscular injection in dogs MSA01 MSA02 MSA05 Time Mean Standard Mean Standard Mean Standard (day) (ng/mL) deviation (ng/mL) deviation (ng/mL) deviation 0 0.0 0.0 0.0 0.0 0.0 0.0 0.04 0.0 0.0 0.6 0.2 0.5 0.1 0.08 0.1 0.1 0.8 0.1 1.4 0.8 0.17 0.6 0.1 2.0 0.6 2.8 1.3 0.25 1.5 0.2 3.7 0.9 3.5 3.7 1 7.0 5.0 15.6 1.4 14.2 10.3 3 10.1 5.4 16.8 5.7 12.7 8.0 7 16.1 12.4 11.6 4.3 11.9 7.8 10 14.2 6.0 14.1 4.1 11.9 6.0 14 14.4 1.9 14.7 3.1 10.1 4.8 21 10.6 1.5 15.2 4.9 6.6 3.8 28 9.3 4.4 11.8 1.5 6.7 3.4 35 5.3 1.6 8.4 4.5 6.0 3.0 42 4.9 2.4 4.4 0.8 4.1 2.3 49 5.8 5.2 1.7 0.6 4.2 3.0 56 1.6 1.3 0.7 0.9 2.5 1.3 63 1.4 1.1 0.4 0.7 3.1 1.2 70 0.5 0.7 0.0 0.0 2.5 1.1 77 0.6 0.6 0.3 0.5 2.4 1.2 84 0.5 0.7 0.0 0.0 1.9 1.1 91 0.4 0.4 0.1 0.2 0.9 1.0

Example 12: Pharmacokinetic Profile of PLGA-Based Formulations in Rats

The PLGA-based formulations, PS03 and PS10, as prepared in Example 6 were injected subcutaneously or in SD male rats at a dose of 60 mg/kg buprenorphine equivalent. The pharmacokinetic profile results are shown in FIG. 37 and Table 25.

TABLE 25 Mean plasma buprenorphine levels after intramuscular injection in rats PS03 PS10 Time Mean S.D. Time Mean S.D. (days) (ng/mL) (n = 3) (days) (ng/mL) (n = 4) 0 0.00 0.00 0 0.00 0.00 0.021 0.070 0.12 0.042 2.67 0.23 0.042 0.690 0.38 0.083 4.76 0.87 0.083 1.51 0.78 0.25 10.3 1.63 0.17 3.58 0.92 1 6.98 2.08 0.25 4.07 2.65 3 5.78 1.23 1 1.76 0.33 7 9.39 3.13 3 1.23 0.72 10 8.39 2.73 7 1.66 0.32 14 9.11 4.73 10 2.06 0.23 21 7.31 2.63 14 4.38 1.06 28 8.80 5.57 21 5.02 0.45 35 7.32 3.27 28 4.21 0.26 42 6.22 2.85 35 5.52 1.48 49 5.03 2.03 42 3.09 0.35 56 4.13 1.10 49 2.75 0.32 63 4.75 1.81 56 1.99 0.46 70 4.70 1.69 63 2.23 0.43 77 3.90 0.92 70 2.01 0.38 84 3.27 0.61 77 1.83 0.31 — — — 84 1.09 0.45 — — — 91 1.25 0.22 — — — 98 0.830 0.25 — — — 105 1.09 0.32 — — — 112 1.10 0.29 — — — 119 1.09 0.31 — — — 126 1.04 0.26 — — — 133 1.02 0.44 — — — 140 0.950 0.12 — — — 147 0.870 0.23 — — —

The embodiments described above are intended to be merely exemplary, and those skilled in the art will recognize, or will be able to ascertain using no more than routine experimentation, numerous equivalents of specific compounds, materials, and procedures. All such equivalents are considered to be within the scope of the disclosure and are encompassed by the appended claims. 

What is claimed is:
 1. An injectable pharmaceutical composition, comprising 3-acyl-buprenorphine or a pharmaceutically acceptable salt thereof in a controlled release matrix and a biocompatible solvent, exhibiting a steady release profile lasting over at least one month when injected into a patient or an animal.
 2. The injectable pharmaceutical composition according to claim 1, wherein the controlled released matrix is selected from poly(lactide-co-glycolide), sucrose acetoisobutyrate, lecithin, diolein or a combination of two or more thereof.
 3. The injectable pharmaceutical composition according to claim 1, wherein the biocompatible solvent is selected from the group consisting of N-methyl-2-pyrrolidone, ethyl acetate, ethanol, butanol, 2-butanol, isobutanol, isopropanol, glycerin, benzyl benzoate, dimethyl sulfoxide, N,N-dimethylacetamide, propylene glycol, dimethyl glycol, benzyl alcohol, and a combination of two or more thereof.
 4. The injectable pharmaceutical formulation according to claim 1, wherein the 3-acyl-buprenorphine has an acyl group having a straight chain or a branched chain alkyl portion of 1 to 17 carbon atoms.
 5. An injectable sustained release microspheres formulation comprising a pharmaceutically effective amount of 3-acyl-buprenorphine or a salt form thereof encapsulated with poly(lactide-co-glycolide) suspended in an aqueous diluent, exhibiting a steady release profile lasting over at least one month when injected into a patient or an animal.
 6. The injectable sustained release microspheres formulation according to claim 5, wherein the 3-acyl-buprenorphine has an acyl group having a straight chain or a branched chain alkyl portion of 1 to 17 carbon atoms. 